Upon further investigation, they discovered that people with the highest levels of perfluoroalkyl substances (PFAS), especially women, had gained the most weight. PFAS are man-made chemicals used to make products more stain-resistant, waterproof or nonstick, and they are found on pots, pans and some fast food wrappers.

“These findings suggest that environmental chemicals may play a role in the current obesity epidemic. Given the persistence of these PFAS in the environment and the human body, their potential adverse effects remain a public health concern,” the researchers wrote.

While scientists aren’t exactly sure why PFAS could cause weight gain, they noted that people with higher levels of PFAS also had a lower resting metabolic rate. In other words, they were burning fewer calories throughout the day while doing normal activities.